Screw clamp with a head having a reverse-acting and renewable gripping surface



Aug. 30, 1966 E. M. GARDNER 3,269,766

SCREW CLAMP WITH A HEAD HAVING A REVERSE-ACTING AND RENEWABLE GRIPPING SURFACE Filed Oct. 5, 1964 INVENTOR` Edward Merrill Gardner AT ORNEYS United States Patent O 3 269 766 SCREW CLAMr wrirn A HEAD HAvnsG A REVERSE-ACTING AND RENEWABLE GRIP- PING SURFACE Edward Merrill Gardner, Flushing, NY., assignor to Merrill Brothers, Maspeth, NY., a corporation of New York Filed Oct. 5, 1964, Ser. No. 401,562 12 Claims. (Cl. 294-101) This invention relates to improvements in screw-type lifting clamps, particularly with respect to the parts of the clamp engaging the steel plate or other article to be lifted.

Screw clamps are preferred by some for lifting heavy plates but as far as known, such clamps simply include a screw mounted in one jaw of the clamp having a slightly oval-shaped end facing a gripping pad mounted in fixed position in the opposite jaw of the clamp. While the pad may include the usual serrations, it is often difficult to tighten the screw enough to hold a plate or to tell whether or not the screw has been tightened sufficiently to prevent the clamp from slipping off a steel plate during lifting.

Accordingly, the primary object of the present invention is to provide a screw type lifting clamp in which the screw is provided with a special type of gripping head which prevents any appreciable slipping, even though the screw is brought up to merely hand or finger tightness.

A further object of the invention is to provide a screw type clamp of simple and inexpensive construction, adapted to take a wide range of plate thicknesses.

A further object of the invention is to provide a clamp which may be positively locked on the plate without any dependence on springs or levers.

According to the invention, the improved screw type clamp comprises a screw in one jaw carrying a rotatably and pivotally mounted plate-engaging member having a convex serrated gripping surface and connected to the inner end of the screw by a Iball and socket joint. The clamp further includes a serrated gripping pad preferably slidably and rotatably mounted in the jaw facing the .gripping member or head on the screw.

The pivoted and rotatable gripping head and the slidable and rotatable gripping pad cooperate with each other to provide a safe and dependable clamp which may be secured by hand tightening, and which functions so that on lifting a heavy steel plate, the swiveled gripping head pivots on the ball end of the screw simultaneously with the sliding movement of the pad on the object being lifted to provide a powerfully-wedged `gripping action. Both may also rotate.

The pivoted lhead on the end of the screw advantageously includes a convex plate-gripping surface having concentric circular teeth stepped back from the center of the face of the head. As a plate is lifted, the head rolls on the ball of the screw and these teeth move successively into engagement with the plate under extreme increasing pressures.

The clamp, which may be secured by a hand operation of the screw, may carry such a heavy load that the pivoted head is pivoted and rotated so that several teeth come into engagement with the plate. When a plate has been lifted to the desired position and let down, the clamp is easily released because of the slidable pad and the stress in the clamp which tends to force the pad backwardly or upwardly, or in a direction to relieve the stress, thereby allowing the pivoted head of the screw to move to a less tight position where the screw is readily unscrewed by hand.

One purpose and feature of this clamp is that it may be used on either red hot or cold steel plates, billets, ingots ice and the like by simply reversing or shifting one area of the gripping head to gripping position for hot work. The other areas will havethe hardness of the teeth preserved by not being overheated and, therefore, still usable on cold metal pieces or assemblies.

Another purpose or object is to provide a gripping head which will grip the plate if it tends to slip in any direction. This quality or characteristic is vital to holding a plate of relatively -great thickness when lifting or pulling horizontally and then changing to vertical or vice versa. On my clamp, the reverse action on the gripping head and pad causes instant gripping pressure and does not allow the opposing pad to slide off toward the edge of the plate; My clamp eliminates very simply the many problems to prevent a clamp from coming off a plate when lifting from horizontal to vertical, particularly on a wide grip. Also, this feature enables the gripping of a fabricated plate when on a 45 angle or more on edge to the lifting direction. The cam on conventional clamps will not function here and a screw clamp without the gripping head will not hold a very heavy plate in any position.

Another feature of my invention is to provide an automatic centralizing means for the pivoted gripping head, for example, it may be composed of several spring loaded protruding plungers. This is particularly useful in hot plate lifting where a man cannot hold the gripping head up and where on hot metal the teeth do not slip so as to centralize themselves as they do on cold metal.

The invention includes other details, features and advantages described hereinafter in connection with the accompanying drawings illustrating a preferred embodiment of the improved screw clamp.

In the drawings:

FIG. 1 is an elevational side view with parts broken away or in section of a screw type steel plate lifting clamp constructed in accordance with the invention;

FIG. 2 is a broken elevational view of the clamp shown in FIG. l, showing the pivotable head pivoted to ya gripping position on a plate being lifted;

FIG. 3 is an enlarged detailed sectional view showing the structure of the gripping head and the ball and socket joint by which it is mounted on the screw; and

FIG. 4 is a front view to a smaller scale of the gripping y head of the screw.

Referring to FIGS. l and 2 of the drawings, the screwtype lifting clamp illustrated therein comprises a clamp body 10 provided with fixed jaws 12 and 14 spaced apart and facing each other to provide an opening or space 16 for receiving heavy steel plates and the like, for example the plate 18, shown in phantom and prior to the beginning of a lifting operation. The clamp body 10 is drilled at 20 for receiving the pin of a lifting shackle clevis, not shown.

The lower pant of the jalw 14 has a transversely threaded bore carrying a threaded screw 22. The outer end of lche screw has a reduced diameter carrying a shrunk-on lcollar 24 provided with four regularly-spaced holes 26 for receiving a pin for operating the screiw 22. Tlhe inside ofthe jaw 14 is ohaimlfered at 28 to square-up the end of the bore for threading. As in the case of conventional screw-llmting clamps, the inner end of the screw 22 faces toward a gripping pad 32 mounted in the jaw 12. In accordance with an important feature of Iche present invention, the inner end of the screw 22 carries a pivoted `gripping head 34 connected to the inner end of the screrw by a ball and socket joint connection which includes a socket sunfa'ce 36 in the head 34 and a ball 38 on the end ott the screw 22, as illustrated more in detail in FIG. 3. The socket 36 in the gripping head 34 comprises a semi-cylindrical portion fitting the ball 38 and a projecting flange 39 which is slotted at a few points and bent in around the back portion of the ball, so that the gripping head is returned on the ball and capable of being rotated thereon and pivoted through a considerable angle, for example 20 or more, as will be apparent from the shortness of the flange 3-9 and the sperical shape of the portion of the ball l38 connecting with the inner end of the screw 22.

The gripping head 34 comprises a hardened steel member having a cylindrical outer surface 40 and a convex shaped front face provided with concentrically cut gripping teeth, the circular edges of which, outwardly from the axis of the head, are at progressively `greater distances from the center of the ball 318. The gripping teeth are located concentrically with respect to the surface 40 or to the axis at the center of the face of the gripping head and in line with the axis of the screw 22 in the position shown in FIGS. 1, 3 and 4.

The circular teeth on the face o-f the gripping head 314, as shown in FIG. 3, include an inner tooth 41, the edge osf which is located in or denes a plane normal to the axis of the gripping head, this tooth being the inner of a first series extending to and including the tooth 42, the edges of which are all located on a line or sur-tace extending at an angle of about 5 degrees with respect to the plane referred to above. The edge of the tooth 42 is locate-d at an angle of approximately thirty-nine degrees to the axis of the gripping head extending from the center of the lball 38. This tooth 42 comprising the outer of the irst series is also the inner tooth of a second series extending to the edge of the surface 40, which edge and the edges of the second series of teeth are located on a line or surface at an angle of about l5 degrees with respect to the plane referred to above. These relationships are shown in FIG. 3.

The automatic centralizing means for the gripping head comprises a plurality of plungers 43, for example four spaced at equal distances around the outer portion of the gripping head, each including an end portion projecting almost to the line of the plane of the inner tooth 41. Each plunger 43 is 'backed up by a compression spr-ing 44 mounted against an enlarged head on the plunger 43 which lits against a shoulder in the bore of the gripping head 34. The spring is held in place by one or more threaded-in plugs 45.

The ball and socket joint comprising the engaging surfaces of the :ball 38 and the head 34 is lubricated through a du'ct 46 provided with a grease ttting on the back of the head and extending to the axis of the head where it opens out through the surface 36. Grease supplied through the fitting (not shown) is forced under pressure between the sulface 36 and the surface of the ball 38 which Ihas a diameter a few thousandths less than that of the socket.

The gripping pad 32 mounted on the jaw 12 is provided with a serrated face opposite the gripping head 314 and is mounted in an oversized recess 48 cut in the inner face of the jaw 12. The pad 32 includes a lange back surface area engaging the front surface of the recess 48, and a smaller axially-extending shank 50 projecting through an oversized opening 52. The projecting end of the shank extends through a washer 54 and is riveted over at 56, in a counter-sink bore 58, so that the gripping pad is loosely mounted in the jaw 12 and freely slidalble in any direction in the recess 48. The pad 32 may be retained by a nut instead of riveting. The serrations on the front of the pad 32 are concentric sharp projections adapted to bite or cut into a steel plate being gripped and lifted. Tfhe function of the slidalble gripping pad 32 and its cooperation with the pivoted gripping head 34 of the screw 22 are explained hereinafter in connection with a description of the operation of the clamp as a whole.

FIG. l illustrates the position of the clamp as it is placed on a plate 18, for example a steel plate weighing from 3 to 200 tons. In this position of the clamp the operator turns up the screw 22 by hand until it is linger tight, with the inner circular tooth 41 engaging the plate. A hand-tight screw will cause the inner tooth 41 to cut into the plate approximately 0.001 inch or slightly more. The gripping head 314 will automatically assume the position relative to the ball 318, as shown in FIG. 3, and when the crane applies a lifting force to the clamp body 10, in the direction of the arrow in FIG. 2, the head 34 starts to pivot on the ball 318, and simultaneously the pad 32 slips to the bottom of the recess 48. This may continue until the gripping head 34 pivots to the position shown in FIG. 2 and the gripping pad 32 is at the bottom of the recess 48.

From the relationship shown in FIG. 3, it will be apparent that since the edges of the teeth outwardly of the axis of the head 34 are progressively farther away from the center of lthe ball 318, they will engage, cut more deeply into lthe plate 18 and increase the gripping pressure, as the plate is lifted. During the lifting of the plate, the front of the head 34 is pulled downwardly because of the low angle of engagement of the point of contact of the rst three teeth with the plate and the center of rotation at the center of the ball 38. The pad 32 may be regarded as holding a large part of the load when the parts reach the position shown in FIG. 2, because it is supported directly on the bottom of the recess 48 with its teeth penetrating the plate. Some slippage does, in fact, occur on the pad as the head pivots dolwn farther, s0 that the surface of the plate may be torn slightly by the teeth on the pad until the gripping head 34 reaches a maximum wedging position sufficient to hold the plate.

During the lifting operation, the spreading force caused by the tilting of the gripping head 34 puts the jaws of the clamp under a considerable strain and they, in fact, are stressed to such an extent that they spread apart slightly.

After a plate has been lifted and set down in the desired position, it might appear that the clamp would be so jammed on the plate that its release would be extremely diicult. However, when the clamp is not carrying the weight of the plate, the stress between the jaws of the clamp is so great that it has a tendency to pivot the gripping head to a less tight position, for example, upwardly and to slide the gripping pad 32 upwardly relative to the body of the clamp. When the gripping head 34 moves in this way, the gripping pressure is released and it is possible to release the screw 22 by hand. If desired, a bar may be inserted in one of the holes 26 for either tightening or release, or a pin-wrench may be applied to one or more of the Aholes 26, but usually these expedients are unnecessary and are only used as precautionary measures when the clamp is used for lifting very heavy steel plates.

The clamp is quite easy to apply to a plate to be lifted. For example, the screw 22 is merely retracted until the gap between the head 34 and jaw 12 is adequate for the thickness of the plate. Then the clamp is set on the plate so that, for example, it rests on the top edge of the plate, after which the screw 22 is tightened merely by finger tightening, until and after the axis of the head 34 is in line with the axis of the screw 22. Following this, the lifting operation is carried out as described above.

The gripping head 34 is readily swiveled on the ball 38, which may be covered with lubricant as described above, so that when the circular tooth 41 hits the plate 18 due to the slipping under no load, at the carefully designed angle of contact, the rst tooth will slide on the plate until it engages the plate on its entire circumference. This first tooth will then start to imbed in the plate. The clamp functions in this manner on cold plates, but on hot metal the spring-loaded plungers are relied on to center the gripping head with respect to the screw.

If certain areas of the teeth `become dull, which they do with continued use on hot metal pieces, the head 34 may be rotated by hand, so that the sharpest portions of the teeth are at the top. The head is then held while the screw 22 is rotated to force the head into engagement with the plate.

The improved screw clamp of the present invention with its swiveled ball-and-socket jointed gripping head and cooperating slidable gripping pad is an unusual safety clamp, for lifting heavy steel plates, ingots and the like, which does not depend on springs or levers, but is provided with a positive screw attaching and wedging grip arrangement. As an example of the effectiveness of the clamp construction of the present invention, a conventional screw clamp with a xed gripping pad was placed on a 12 ton steel plate, and the end of the screw brought into engagement with the side of the plate to grip the plate in the clamp. It was found that this clamp required a 160 pound man to lay his entire weight on a six foot wrench on the end of the screw in order to hold the 12 ton plate. With plates of greater weight, the clamp simply did not hold but slipped off. In contrast, the clamp of the present invention was applied to plates of different weight by simply tightening the screw with one hand. Plates of up to 400,000 pounds were lifted and the heavier the plate to which the clamp is applied, the tighter the clamp became on the plate because of the wedging toggle action referred to above.

The pivoted toggle-acting gripping head, after the screw is brought up to hand tightness, places the clamp under a terric strain because of the wedging action, so that the body of the clamp is actually stressed or put under stress during a lifting operation. Furthermore, this is accomplished with very little manual force, as compared to the force required where a six-foot wrench must be used to tighten the clamp to just lift 12 tons, and an impossibility to lift 200 tons which my clamp has lifted. In fact, it is impractical to operate any previously known clamp on over 100 tons Where the clamp must be applied vertically, horizontally, and upsidedown on thick, heavy plates varying greatly in thickness, that is, plates or the like from 6 to 15 inches thick.

While the swiveled gripping head 34 and the slidable pad 32 cooperate to give an unusual gripping action and an easily releasable clamp, the pivoted and rotatable gripping head 34 can be used in screw clamps provided with xed gripping pads, but the release of the clamp after lifting the plate is, of course, more difficult, and it will in many cases be almost impossible to release the clamp. The old type screw clamps may be rebuilt to install a slidable gripping pad and machine the end of the screw to provide a ball and then apply a swiveled gripping head, such as that shown in FIG. 3 of the drawings.

The gripping head 34 as pivotally mounted on the inner end of the screw 22 has a number of advantages, some of which are as follows:

(1) The diameter of the head is substantially greater than that of any screw 22 ordinarily used and thereby provides a larger and superior gripping surface.

(2) The swiveled head 34 may be advanced by the screw 22 to a position so that the pivot center is located closely adjacent to the plate to be lifted, thereby providing a more effective toggle action when a lifting force is applied to the hand-tightened clamp.

(3) The generally convex shape of the face of the gripping head 34 is such that during lifting and pivoting of the head on the ball 38, teeth are successively brought into engagement with the plate being lifted, the edges of which are at progressively greater distances from the center of the ball 38, and progressively increase the gripping stress on the plate.

(4) The stepped-back arrangement of the concentrically arranged teeth on the gripping head provides progressively greater tooth arc engagement with the plate because of the progressively greater diameters of the circular teeth outwardly from the axis of the head.

(5) The convex curvature of the face of the gripping head 34 is such as to provide ample wedging grip for lifting the heaviest plate for which the clamp is made and place ample stress in the clamp without causing the head to be rotated off the ball 38. In other words, the difference in distance between the edge of the inner tooth 41 and the edges of the outer teeth from the center or surface of the ball 38 is such as to completely stress the clamp to hold the plate without permitting rotation of the gripping head to an extent that it would roll olf the ball 38 and release the plate.

I claim:

1. In a screw clamp of the type used for lifting steel plates including a body having spaced opposed projecting jaws defining a U-shaped structure and providing a platereceiving space between the jaws open at the projecting ends of the jaws, said space being adapted for receiving a steel plate to be gripped by the clamp and lifted, a screw threaded through one of said jaws toward the other jaw, and a gripping pad carried by said other jaw and having a gripping surface facing said screw across said space, the improvement including a gripping head having a serrated convex plate-gripping surface and being pivotally mounted by a ball and socket joint on the inner end of said screw with its convex gripping surface facing toward the gripping surface of the pad, the gripping head being symmetrical about its center so that its gripping functions are effective equally well by a motion of the plate inwardly or outwardly and with the first serrations at a suiciently low angle as measured through the center of the ball to the surface of the plate so that a slipping of the plate will cause rotation of the head off center and a gradual increase in succeeding teeth in the distance from the center of the ball to -their contact point to effect further rotation of the head with further penetration of teeth until the desired point is reached where rotation of the head is stopped by rapidly increased distances ofthe contact points of the teeth to the center of the ball at which point jamming of the gripping head with positive gripping of the plate takes place.

2. A clamp as claimed in claim 1, in which the first serration near the center of the gripping surface of the head has an included angle from diametrically opposite points thereon to the center of rotation as the vertex of the angle so as to cause the head to center itself against the plate.

3. A clamp as claimed in claim 1, including a multiplicity of positions on the gripping head as gripping teeth which are moved to gripping position by rotating the head.

4. A clamp as claimed in claim 1, in which said pad is slidably mounted relative to the inner face of the jaw in which it is mounted and freely movable lengthwise thereof with a plate jammed in the clamp when the lifted plate is brought to rest and the lifting force on the clamp released, thereby permitting pivoting of the gripping head on the screw toward a less tight position and the ready operation of the screw for loosening the grip of the clamp on the plate.

5. A clamp as claimed in claim 1, in which the jaw carrying the gripping pad includes a surface facing toward the other jaw, said surface including an elongated recess extending lengthwise of the jaw in which the gripping pad is slidable.

6. A clamp as claimed in claim 5, in which the gripping pad includes a head located in said recess and having a serrated portion projecting from the inner surface of the jaw in which the pad is mounted, and a shank on the back of the head extending into said jaw and movable lengthwise of the jaw in an elongated slot in the back of said recess.

7. A clamp as claimed in claim 1, wherein said gripping head comprises a member carrying said gripping surface which constitutes a substantially convex segment the arc of which is substantially greater than the radius of the ball of the ball and socket joint, said gripping surface being provided with a series of gripping teeth arranged outwardly with respect to the axis of the gripping head, the axis of the gripping head being located on the axial 7 line of the screw when the gripping head is in its normal position on the ball of the ball and socket joint, and said head being rotatable on said ball to bring teeth farther out from the axis of the gripping head into engagement with a steel plate being lifted by the clamp.

8. A clamp as claimed in claim 1, including centralizing spring means for automatically centralizing the gripping head with the axis of the screw.

9. In a screw clamp to the type used for lifting steel plates including a body having spaced opposed projecting jaws defining a U-shaped structure and providing a platereceiving space between the jaws open at the projecting ends of the jaws, said space being adapted for receiving a steel plate to be gripped by the clamp and lifted, a screw threaded through one of said jaws toward the other jaw, and a gripping pad carried by said other jaw and having a gripping surface facing said screw across said space, the improvement including a gripping head having -a serrated convex plate-gripping surface and being pivotally mounted by a ball and socket joint on the inner end of `said screw with its convex gripping surface facing toward the gripping surface of the pad, said gripping head comprising a member carrying said gripping surface which constitutes a substantially convex segment the arc of which is substantially greater than the radius of the ball of the ball and socket joint, said gripping surface being provided with a series of gripping teeth arranged outwardly with respect to the axis of the gripping head, the axis of the gripping head being located on the axial line of the screw when the gripping head is in its normal position on the ball of the ball and socket joint, and said head being rotatable on said ball `to bring teeth farther out from the axis of the gripping head into engagement with a steel plate being lifted by the clamp.

10. A screw clamp as claimed in claim 9, in which said Cit 3 gripping head is of substantially larger diameter than that of the screw and in which the convex plate gripping surface of said segment is provided with a series of concentrically arranged spaced circular teeth the edges of which are located at progressively grea-ter distances from the center of the ball of the ball and socket joint.

11. A screw clamp as claimed in claim 9, in which the convex gripping surface of the gripping head includes a series of spaced concentric gripping tee-th arranged concentrically with respect to the axis of the gripping head and with respect to the axis of the screw when the head is symmetrically located on the screw, and in which said screw is adapted to advance the gripping head in-to close proximity to the steel plate to be lifted, whereby said gripping head is rotated relative to the center of the ball of the ball and socket joint when in close proximity to the steel plate `being gripped `and lifted by the clamp.

12. A screw clamp as claimed in claim 9, in which the gripping pad is slidably mounted relative -to the inner face of the jaw in which it is mounted and freely movable lengthwise, and slidable pad cooperating with the rotatable gripping head to move with the plate during the rotation of the head.

References Cited by the Examiner UNITED STATES PATENTS 2,548,401 4/1951 Sherwood 294-103 FOREIGN PATENTS 322,410 7/1957 Switzerland.

GERALD M. FORLENZA, Prima/'y Examiner.

G. F. ABRAHAM, Assistant Examiner. 

1. IN A SCREW CLAMP OF THE TYPE USED FOR LIFTING STEEL PLATES INCLUDING A BODY HAVING SPACED OPPOSED PROJECTING JAWS DEFINING A U-SHAPED STRUCTURE AND PIVOTING A PLATERECEIVING SPACE BETWEEN THE JAWS OPEN AT THE PROJECTING ENDS OF THE JAWS, SAID SPACE BEING ADAPTED FOR RECEIVING A STEEL PLATE TO BE GRIPPED BY THE CLAMP AND LIFTED, A SCREW THREADED THROUGH ONE OF SAID JAWS TOWARD THE OTHER JAW, AND A GRIPPING PAD CARRIED BY SAID OTHER JAW AND HAVING A GRIPPING SURFACE FACING SAID SCREW ACROSS SAID SPACE, THE IMPROVEMENT INCLUDING A GRIPPING HEAD HAVING A SERRATED CONVEX PLAT-GRIPPING SURFACE AND BEING PIVOTALLY MOUNTED BY A BALL AND SOCKET JOINT ON THE INNER END OF SAID SCREW WITH ITS CONVEX GRIPPING SURFACE FACING TOWARD THE GRIPING SURFACE OF THE PAD, THE GRIPPING HEAD BEING SYMMETRICAL ABOUT ITS CENTER SO THAT ITS GRIPPING FUNCTIONS ARE EFFECTIVE EQUALLY WELL BY A MOTION OF THE PLATE INWARDLY OR OUTWARDLY AND WITH THE FIRST SERRATIONS AT A SUFFICIENTLY LOW ANGLE AS MEASURED THROUGH THE CENTER OF THE BALL TO THE SURFACE OF THE PLATE SO THAT A SLIPPING OF THE PLATE WILL CAUSE ROTATION OF THE HEAD OFF CENTER AND A GRADUAL INCREASE IN SUCCEEDING TEETH IN THE DISTANCE FROM THE CENTER OF THE BALL TO THEIR CONTACT POINT TO EFFECT FURTHER ROTATION OF THE HEAD WITH FURTHER PENETRATION OF TEETH UNTIL THE DESIRED POINT IS REACHED WHERE ROTATION OF THE HEAD IS STOPPED BY RAPIDLY INCREASE DISTANCES OF THE CONTACT POINTS OF THE TEETH TO THE CENTER OF THE BALL AT WHICH POINT JAMMING OF THE GRIPPING HEAD WITH POSITIVE GRIPPING OF THE PLATE TAKES PLACE. 